In my view one of the biggest limitations of HTML is that the page cannot be broken down into re-usable elements. Typically for example the header, footer and navigation in a web page is the same for most of the pages in a web site. This makes it easier for the user to find information and find their way around the site.
In order to avoid unecessary duplication of code, it is important that web pages can be broken down into parts. DreamWeaver does this using HTML comments which it processes into HTML. Visual Studio has a better way, but the mechanism differs between Web Forms and MVC
Web Forms is not as flexible as MVC and uses Master pages. However to avoid duplication in bigger sites, master pages need to be nested. This site is using nested master pages.